Diagnosis Hydroids colonial, stolonal or branching, covered by perisarc infested with foreign material; filmy perisarc also envelops hydranth body and basal part of tentacles; hydranths with one whorl of filiform tentacles; gonophores arise singly from hydranth pedicels, liberated as free medusae.
Medusa with eight clusters of marginal tentacles, all tentacles similar in structure; with or without ocelli; with four dichotomously branching oral tentacles; gonads in perradial or adradial position. [details]